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><H1
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><A
NAME="CONFIG-SETTING"
>18.1. Setting Parameters</A
></H1
><P
>    All parameter names are case-insensitive. Every parameter takes a
    value of one of five types: Boolean, integer, floating point,
    string or enum. Boolean values can be written as <TT
CLASS="LITERAL"
>on</TT
>,
    <TT
CLASS="LITERAL"
>off</TT
>, <TT
CLASS="LITERAL"
>true</TT
>,
    <TT
CLASS="LITERAL"
>false</TT
>, <TT
CLASS="LITERAL"
>yes</TT
>,
    <TT
CLASS="LITERAL"
>no</TT
>, <TT
CLASS="LITERAL"
>1</TT
>, <TT
CLASS="LITERAL"
>0</TT
>
    (all case-insensitive) or any unambiguous prefix of these.
   </P
><P
>    Some settings specify a memory or time value.  Each of these has an
    implicit unit, which is either kilobytes, blocks (typically eight
    kilobytes), milliseconds, seconds, or minutes.  Default units can be
    found by referencing <TT
CLASS="STRUCTNAME"
>pg_settings</TT
>.<TT
CLASS="STRUCTFIELD"
>unit</TT
>.
    For convenience,
    a different unit can also be specified explicitly.  Valid memory units
    are <TT
CLASS="LITERAL"
>kB</TT
> (kilobytes), <TT
CLASS="LITERAL"
>MB</TT
>
    (megabytes), and <TT
CLASS="LITERAL"
>GB</TT
> (gigabytes); valid time units
    are <TT
CLASS="LITERAL"
>ms</TT
> (milliseconds), <TT
CLASS="LITERAL"
>s</TT
>
    (seconds), <TT
CLASS="LITERAL"
>min</TT
> (minutes), <TT
CLASS="LITERAL"
>h</TT
>
    (hours), and <TT
CLASS="LITERAL"
>d</TT
> (days).  Note that the multiplier
    for memory units is 1024, not 1000.
   </P
><P
>    Parameters of type <SPAN
CLASS="QUOTE"
>"enum"</SPAN
> are specified in the same way as string
    parameters, but are restricted to a limited set of values.  The allowed
    values can be found
    from <TT
CLASS="STRUCTNAME"
>pg_settings</TT
>.<TT
CLASS="STRUCTFIELD"
>enumvals</TT
>.
    Enum parameter values are case-insensitive.
   </P
><P
>    One way to set these parameters is to edit the file
    <TT
CLASS="FILENAME"
>postgresql.conf</TT
>,
    which is normally kept in the data directory.  (A default copy is
    installed there when the database cluster directory is
    initialized.)  An example of what this file might look like is:
</P><PRE
CLASS="PROGRAMLISTING"
># This is a comment
log_connections = yes
log_destination = 'syslog'
search_path = '"$user", public'
shared_buffers = 128MB</PRE
><P>
    One parameter is specified per line. The equal sign between name and
    value is optional. Whitespace is insignificant and blank lines are
    ignored. Hash marks (<TT
CLASS="LITERAL"
>#</TT
>) designate the rest of the
    line as a comment.  Parameter values that are not simple identifiers or
    numbers must be single-quoted.  To embed a single quote in a parameter
    value, write either two quotes (preferred) or backslash-quote.
   </P
><P
>    
    In addition to parameter settings, the <TT
CLASS="FILENAME"
>postgresql.conf</TT
>
    file can contain <I
CLASS="FIRSTTERM"
>include directives</I
>, which specify
    another file to read and process as if it were inserted into the
    configuration file at this point.  Include directives simply look like:
</P><PRE
CLASS="PROGRAMLISTING"
>include 'filename'</PRE
><P>
    If the file name is not an absolute path, it is taken as relative to
    the directory containing the referencing configuration file.
    Inclusions can be nested.
   </P
><P
>    
    The configuration file is reread whenever the main server process receives a
    <SPAN
CLASS="SYSTEMITEM"
>SIGHUP</SPAN
> signal (which is most easily sent by means
    of <TT
CLASS="LITERAL"
>pg_ctl reload</TT
>). The main server process
    also propagates this signal to all currently running server
    processes so that existing sessions also get the new
    value. Alternatively, you can send the signal to a single server
    process directly.  Some parameters can only be set at server start;
    any changes to their entries in the configuration file will be ignored
    until the server is restarted.
   </P
><P
>    A second way to set these configuration parameters is to give them
    as a command-line option to the <TT
CLASS="COMMAND"
>postgres</TT
> command, such as:
</P><PRE
CLASS="PROGRAMLISTING"
>postgres -c log_connections=yes -c log_destination='syslog'</PRE
><P>
    Command-line options override any conflicting settings in
    <TT
CLASS="FILENAME"
>postgresql.conf</TT
>.  Note that this means you won't
    be able to change the value on-the-fly by editing
    <TT
CLASS="FILENAME"
>postgresql.conf</TT
>, so while the command-line
    method might be convenient, it can cost you flexibility later.
   </P
><P
>    Occasionally it is useful to give a command line option to
    one particular session only. The environment variable
    <TT
CLASS="ENVAR"
>PGOPTIONS</TT
> can be used for this purpose on the
    client side:
</P><PRE
CLASS="PROGRAMLISTING"
>env PGOPTIONS='-c geqo=off' psql</PRE
><P>
    (This works for any <SPAN
CLASS="APPLICATION"
>libpq</SPAN
>-based client application, not
    just <SPAN
CLASS="APPLICATION"
>psql</SPAN
>.) Note that this won't work for
    parameters that are fixed when the server is started or that must be
    specified in <TT
CLASS="FILENAME"
>postgresql.conf</TT
>.
   </P
><P
>    Furthermore, it is possible to assign a set of parameter settings to
    a user or a database.  Whenever a session is started, the default
    settings for the user and database involved are loaded.  The
    commands <A
HREF="sql-alterrole.html"
>ALTER ROLE</A
>
    and <A
HREF="sql-alterdatabase.html"
>ALTER DATABASE</A
>,
    respectively, are used to configure these settings.  Per-database
    settings override anything received from the
    <TT
CLASS="COMMAND"
>postgres</TT
> command-line or the configuration
    file, and in turn are overridden by per-user settings; both are
    overridden by per-session settings.
   </P
><P
>    Some parameters can be changed in individual <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
>
    sessions with the <A
HREF="sql-set.html"
>SET</A
>
    command, for example:
</P><PRE
CLASS="SCREEN"
>SET ENABLE_SEQSCAN TO OFF;</PRE
><P>
    If <TT
CLASS="COMMAND"
>SET</TT
> is allowed, it overrides all other sources of
    values for the parameter. Some parameters cannot be changed via
    <TT
CLASS="COMMAND"
>SET</TT
>: for example, if they control behavior that
    cannot be changed without restarting the entire
    <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> server.  Also,
    some <TT
CLASS="COMMAND"
>SET</TT
> or <TT
CLASS="COMMAND"
>ALTER</TT
> parameter modifications
    require superuser permission.
   </P
><P
>    The <A
HREF="sql-show.html"
>SHOW</A
>
    command allows inspection of the current values of all parameters.
   </P
><P
>    The virtual table <TT
CLASS="STRUCTNAME"
>pg_settings</TT
> also allows
    displaying and updating session run-time parameters;  see <A
HREF="view-pg-settings.html"
>Section 45.62</A
> for details and a description of the
    different variable types and when they can be changed.
    <TT
CLASS="STRUCTNAME"
>pg_settings</TT
> is equivalent to <TT
CLASS="COMMAND"
>SHOW</TT
>
    and <TT
CLASS="COMMAND"
>SET</TT
>, but can be more convenient
    to use because it can be joined with other tables, or selected from using
    any desired selection condition. It also contains more information about
    what values are allowed for the parameters.
   </P
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